Recent outbreaks of pathogenic E. Coli 0157:H7 poisoning in humans from the ingestion of tainted meats has created great interest in establishing rational and scientifically tested criteria for approving meat and poultry for human consumption. At the present time, most methods in use providing the necessary selectivity and sensitivity necessary to detect the presence of pathogenic bacteria in or on beef or poultry require 24-48 hr's. Test that take this long are based upon classical bacteriological techniques that require samples taken from beef or poultry be grown up in cultures for bacteriological identification and quantification. A new instrument that utilizes the polymerase chain reaction (PCR) for bacterial identification is being marketed by Dupont under the trade name Ribo-Printer. This instrument/method takes at least 8 hours to obtain a result.
In "Biological Particle Identification Apparatus" invented by Gary C. Salzman, Charles T. Gregg, W. Kevin Grace, Richard D. Hiebert, U.S. Pat. No. 4,884,886 awarded in Dec. 5, 1989, these inventors show that multiparameter light scattering measurements can be used to identify biological particles such as bacteria and viruses in pure homogeneous solutions. This requires that each of the particles to be identified be purified prior to analysis. This technique cannot work with heterogeneous samples and is therefore unsuitable for quickly identify and quantify bacterial pathogens in beef menstrua in the slaughterhouse.
In "Detection And Identification of Bacteria By Means Of Ultra-Violet Excited Resonance Raman Spectra", invented by Wilfred H. Nelson, Richard A. Dalterio, and Sperry Peacedale, U.S. Pat. No. 4,847,198, awarded on Jul. 11, 1989 these inventors have shown that resonance Raman spectra of pure cultures of bacteria exhibit taxonomic identifiers. By collecting resonance Raman spectra as a function of laser excitation frequency, these inventors claim a method of taxonomic identification using the excitation behavior of the Raman spectra of the species in question. The excitation behavior is the behavior of the resonance Raman spectra of the same sample as the excitation frequency is varied. These inventors used a quartz capillary as a sample holder through which the analyte solution was flowed, and upon which the laser excitation beam was impinged. The Raman light can be collected in a geometry from 0 to 90 degrees from the collection optical axis.
What this solution gives with one hand it takes away with the other. The design of the Raman system in this patent is subject to spectral artifacts due to laser induced photodecomposition of the quartz capillary, as well as denaturation and photodecomposition of the biomolecules at the quartz-liquid interface. This may cause changes in the biomolecules' resonance Raman spectra. Furthermore, this invention doesn't include a polarization scrambler at the entrance to the monochrometer. The lack of a polarization scrambler can lead to anomalous spectra, because the gratings and mirrors in a monochrometer preferentially pass light of a given polarization with higher relative efficiency than another polarization. A grating monochrometer therefore, exhibits polarization bias that must be removed if the results from one monochrometer configuration can be compared to another. Furthermore, when comparing spectra or the absolute differential Raman cross-sections of Raman bands obtained at different excitation frequencies, a depolarizer must be employed so that the observed changes in these observables remain unaffected by the polarization bias of the monochrometer. Thus, the excitation behavior of resonance Raman spectra and the absolute differential Raman cross-sections of the Raman bands in the spectra are reliable only if a depolarizer is used in conjunction with a grating monochrometer.